Question

I would like to define an empty list, then add items to the list. Does python 2.6 or 2.7, which I run, support this and what is the syntax?

Thanks,

My real name is Sigurd

Answer 1

Something like
newlist = []

Answer 2

you can add items to a list, including an empty list, using
new_list.append()

the argument you put in the ( ) will be added as the next entry in the list.

Answer 3

I am struggling with this question on CodeAcademy Write a for loop that populates square_list with items that are the square (x ** 2) of each item in start_list.
I tried this:
start_list = [5, 3, 1, 2, 4]
square_list = start_list
for number in square_list:
square = number **2
square_list.append(square)
print square_list

What I don't get is how you populate one array from another one.

Answer 4

yes, that one got me at first too :)

You have to pull FROM the start_list to get the numbers that are then squared.

Try this:

for number in start_list:
square = number**2
square_list.append(square)

Answer 5

I did do that first and it told me square_list is not defined, so I did this:
start_list = [5, 3, 1, 2, 4]
square_list = start_list
for number in square_list:
square = number **2
square_list.append(square)
print square_list
--It goes on and on!

Answer 6

you can define square_list like this:

square_list = []

Then do the for loop with "for number in start_list:"

Answer 7

that will step through each of the 5 numbers in start_list, and inside the for loop, it will square them each and assign them to "square"... your append statement is fine.

The only problems I see are
1) you need to modify the step where you set square_list = start_list... instead, set it equal an empty list like "square_list = [ ]"
and 2) your for loop needs to be "for number in start_list"

Answer 8

Bingo! That did it. Many Thanks JakeV8. It was that darn for number part that I read a dozen times but never saw my error. It worked for real, now we'll see if Codeacademy likes it! Thanks again.
-dan

Answer 9

Glad to help! Hope it works!

Answer 10

also the list comprehension:
square_list = [x**2 for x in start_list]
it does the same thing, but more fun...or not.

Answer 11

@snark Thanks! I wasn't aware you could use the "for x in list" structure inside a list bracket, but that's pretty nice -- gets it all done in one line.